Many devices utilize mercury in their operation, particularly in the field of electric lamps and lighting. Such devices include arc discharge lamps which typically employ mercury as one of the vaporizable components therein. See, for example, Waymouth, Electric Discharge Lamps, MIT Press 1971 for a description of the basic principles of such lamps.
In U.S. Pat. No. 4,379,252, (the '252 patent), the advantages of utilizing higher than normal levels of .sup.196 Hg in the Hg added to fluorescent lamps are described and include unexpectedly high efficiency gains in light output. The disclosure of this patent is hereby incorporated herein by reference.
The drawback of using this isotope lies in its high cost. For example, using conventional enrichment techniques, mercury which has been enhanced to contain about 35% of the .sup.196 Hg isotope can cost about $500 per milligram. While only sub-milligram quantities of this isotope need be added to an incandescent lamp to afford beneficial results, economic realities always play a part in consumer products. Accordingly, it is easy to understand why more economical methods of obtaining this isotope continue to be sought.
Isotopically enriched mercury can be produced by a number of methods. One method involves photosensitized chemical reactions utilizing elemental mercury and various compounds. The compounds HCl and O.sub.2 react with mercury atoms when the mercury atoms are excited by resonance radiation, in particular, 2537 .ANG. radiation produced in a Hg (.sup.3 -.sup.1 S.sub.o) transition generating isotopically selective reactions. Thus, the Hg compound formed contains Hg enriched in a particular isotope, and the Hg must be separated from the compound into its liquid or free state (i.e., elemental Hg)) in order to recover the isotopically enriched metal.
The following documents are recited as general background information with respect to the subject matter of the present invention. To the extent deemed necessary by artisans of ordinary skill in the art to which this invention pertains, the teachings of these documents are hereby incorporated herein by reference.
Grossman, U.S. Pat. No. 4,713,547;
Grossman et al., U.S. Pat. No. 4,678,550;
Maya, U.S. Pat. No. 4,527,086;
Durbin, U.S. Pat. No. 4,514,363;
Work et al., U.S. Pat. No. 3,379,252;
Botter nee Bergheaud et al., U.S. Pat. No. 3,983,019;
Smith et al., U.S. Patent No. 3,897,331;
Grossman et al., U.S. Ser. No. 815,150, filed Dec. 31, 1985;
European Patent Publication No. 0 281 687, published Sep. 14, 1988, claiming priority of U.S. Ser. No. 947,217, filed Dec. 29, 1986;
European Patent Publication No. 0 280 788, published Sep. 14, 1988, claiming priority of U.S. Ser. No. 947,216, filed Dec. 29, 1986.